Braking of Subway Trains To Generate Power for Electricity Grid

The transit authority in metropolitan Philadelphia is launching a pilot project under which the energy created by braking subway trains will be transferred to a large battery that can then either use the electricity to help power the transit system or sell the power to the region’s electricity grid.

The Southeastern Pennsylvania Transportation Authority (SEPTA), which is installing the battery in one of its 38 transit substations, said the power generated by harnessing the kinetic energy of braking trains can either be used to power accelerating trains or stored for sale to the grid. SEPTA estimated that if the system is installed in all its substations, the agency could eventually cut its electric bills by up to 40 percent and generate millions of dollars a year by selling energy back to the grid. Each train car in the system would be equipped with a generator to harness the power from braking. SEPTA is working with a Philadelphia company, Viridity, to choose a sufficiently large battery and apply smart-grid technology to allocate the power created by the braking trains.